1. Field of the Invention
The present invention relates to an apparatus and a method for preparing a reformed gas, more particularly to a reforming gas preparing apparatus and a method for producing a gas mixture composed of large amounts of hydrogen gas comprising hydrogen and carbon monoxide and/or carbon dioxide and/or methane from a starting gas comprising water vapor and a low-temperature liquefied gas, e.g., LNG or LPG or a hydrocarbon gas, e.g., naptha or methane, or water vapor and an alcohol such as methanol.
2. Description of the Related Art
Heretofore, various reaction apparatus, methods and apparatus for preparing a reformed gas have been proposed for the improvement of reaction results, thermal efficiency and catalyst life resulting from improved responsiveness to load fluctuation, greater compactness and more uniform temperature distribution of the reforming reactor. Although Japanese Patent Laid-open No. 62-216634, for example, discloses an invention relating to a fuel-reforming apparatus having an improved catalyst held at the reaction tube wall, there are no concrete means proposed for holding the catalyst at the wall of the reaction tube. As for a method of holding a catalyst at the wall of a reactor, for example, there is a report published by the U.S. Department of Energy DOE/NBN-300821 which proposes a method wherein powdered Raney nickel catalyst (a nickel/aluminum alloy catalyst) is deposited on a reaction tube wall surface by using a flame spray gun (a spray coating gun with flame). This method, however, is not always advantageous industrially because the applicable shape and space of the reactor are limited due to the use of a high temperature hydrogen/acetylene burner. Japanese Patent Laid-open No. 58-216742 also discloses a process where the reactor is formed by cast forming the alloy that is to be the catalyst, however, it has limitations in the degree of freedom in the construction and in the fabrication because of the honeycomb construction or laminated sheets required for keeping the reactor compact.
As for a reactor which has a wall made of a catalyst or a wall deposited with a catalyst (such reactor being referred to as a tube-wall reactor), the reactor has improved thermal conductivity between catalyst body and heating area compared with that in packed bed type of reactor in which a granular catalyst is packed or a monolithic honeycomb catalyst is stacked, nevertheless, it has problems to be solved for obtaining enough surface area of the catalyst required for the reaction. In order to obtain enough surface area of catalyst deposited on the wall of the tube-wall reactor without decreasing the thermal conductivity of the tube-wall, some means is required to increase the boundary area between the heating and the reforming areas by an alternate stacking of the reactor walls, stacking of many small tubes or stacking of partitioned honeycomb-shaped chambers. In practice, a smaller space volume of the reactor per effective catalyst surface area for the reaction is more advantageous industrially because of the resulting compactness of the reactor. As for the stacking of boundary walls having relatively small spaces formed among them, no methods have been disclosed for depositing catalyst tightly on the surface of these boundary walls under mild conditions.